The present invention provides novel hydroxyaromatic oligomers containing both triazine and oxazoline groups, as well as epoxy resin compositions prepared from said oligomers.
Epoxy resins containing triazine groups are known from Japan Kokai Tokkyo Koho 81 26,925 dated March 16, 1981. However, the preparation of said resins involves the use of the difficult-to-obtain intermediate 2,4,6-trichloro-1,3,5-triazine. Furthermore, coupling of 2,4,6-trichloro-1,3,5-triazine with a diphenol through the chloride groups is difficult and leads to a relatively uncontrollable product mix.
An improved preparation of epoxy resins containing triazine groups is disclosed by Hefner, Jr. (in application Ser. No. 547,537 filed Oct. 31, 1983. The process of this invention uses an easily prepared mixed cyanate of a polyphenol More specifically, the diphenol, such as 4,4'-isopropylidenediphenol (Bisphenol A) is reacted with less than a stoichiometric equivalent of a cyanogen chloride or bromide in the presence of an alkaline agent, such as triethylamine. This provides a mixture of monocyanate, dicyanate, and optionally, unreacted diphenol. Trimerization of this mixture provides hydroxyaromatic oligomers containing the triazine group. The oligomers and unreacted diphenol, if any, are then expoxidized using methods well known in the art. Excellent control over the molecular weight and content of triazine groups is provided by this process. The epoxy resin compositions of this invention possess unusually high thermal stability, however, there is room for improvement in their mechanical properties, specifically tensile strength and elongation.
The hydroxyaromatic oligomers of the present invention contain both triazine and oxazoline groups. The oligomers are prepared by co-oligomerization of a mixed cyanate of a polyphenol with an epoxy resin in the process of the present invention. In the process, the diphenol, such as 4,4'-isopropylidenediphenol (Bisphenol A) is reacted with less than a stoichiometric equivalent of a cyanogen halide in the presence of an alkaline agent, such as triethylamine. This provides a mixture of monocyanate, dicyanate and, optionally, unreacted diphenol. Co-oligomerization of this mixture with the desired amount of an epoxy resin, such as the diglycidyl ether of Bisphenol A, provides hydroxyaromatic oligomers containing both triazine and oxazoline groups. Epoxidation of the oligomers and unreacted diphenol, if any, using methods well known in the art provides the epoxy resin compositions of this invention.
Although included within the scope of this invention, oligomers prepared from co-oligomerization of the mixed cyanate of a diphenol with an epoxy resin wherein the mole ratio of epoxy groups to cyanate groups is less than about 1:10, respectively, are generally insoluble in solvent(s) and/or reactant(s) useful in epoxidation reactions but are useful as thermoset resins. Oligomers prepared from co-oligomerization of the mixed cyanate of a diphenol with an epoxy resin wherein the mole ratios of epoxy groups to cyanate groups are about 1:10 to about 1:40 are most preferred precursors to the epoxy resins of the present invention.
Unreacted diphenol (polyphenol), which is preferably present as a component of the oligomers, is converted to the corresponding diglycidyl ether during the epoxidation of the hydroxyaromatic oligomers. This improves overall processability of the epoxy resin. If desired, extra diphenol can be added prior to epoxidation to increase the diphenol diglycidyl ether content of the finished epoxy resin product. Likewise, extra dicyanate may be added to the cyanate mixture prior to co-oligomerization with an epoxy resin.